THE FIRST RAILROAD BRIDGE: In 1841, the New York, New Haven and Hartford Railroad constructed a two-track bridge over the Harlem River at Park Avenue. The bridge was comprised of four 90-foot-long box-truss spans, three of which were fixed iron spans, while the remaining span was a wooden swing span. In the closed position, the bridge had a clearance of only seven feet above mean high water. Masonry piers supported the four box-truss spans.

Over the years, many ships had graved the pivot pier of the wooden bridge, calling the integrity of the span into question. In 1867, the wooden swing bridge was replaced with an iron drawbridge that provided a vertical clearance of 50 feet. By the 1880's, more than 200 trains a day were crossing the Harlem River rail bridge.

REPLACED BY A SWING BRIDGE: Continued growth in rail traffic, as well as the dredging of the Harlem River Ship Canal, soon made the original railroad bridge obsolete. Alfred P. Boller, who designed swing bridges for vehicular traffic over the Harlem River, worked with the New York, New Haven and Hartford Railroad to devise plans for a four-track swing bridge. The railroad and the City of New York split the construction expenses for the new railroad bridge.

The new span was built in conjunction with an Army Corps of Engineers project to construct the Harlem River Ship Canal, which was to provide a navigable channel between the East River and the Hudson River. It was also constructed in tandem with the Park Avenue railroad viaduct south to East 97th Street. (Previously, the railroad ran through Harlem at grade level.)

While the swing span was being constructed from 1891 to 1893, the railroad constructed a temporary wooden and deck-truss drawbridge north of the existing span, and dismantled the old iron bridge. The temporary drawbridge had a lift span of 103 feet, a width of 19½ feet, and a weight of 1,277 tons.

The new bridge featured a 300-foot-long steel swing span. Two Warren truss spans stood on the Bronx side of the Harlem River. Once again, masonry piers were used to support the spans. To comply with new navigation requirements, the span provided a vertical clearance of 25 feet.

THE NEW LIFT BRIDGE: Between 1954 and 1956, the New York, New Haven and Hartford Railroad constructed the third railroad bridge over the Harlem River. The new bridge, which actually consists of two parallel double-track lift spans measuring 340 feet in length, carries four tracks over the Harlem River. Constructed just south of the existing swing bridge, it provides 25 feet of clearance in the closed position, and 135 feet in the open position.

During the 1960's and 1970's, the Park Avenue Railroad Bridge passed through the hands of several financially ailing railroads, ranging from the New York, New Haven and Hartford Railroad to the Penn Central Railroad. Today, the lift span is operated by the MTA Metro-North passenger railroad.

Recently, the MTA Metro-North Railroad announced a $10 million project to rehabilitate the Park Avenue Railroad Bridge. The bridge control, power and lift systems are now beyond their useful life, and will not be replaced. Instead, the project will remove the moveable elements of the bridge (such as the wire rope and counterweight), and will rehabilitate the foundation. The MTA Metro-North Railroad currently is seeking approval from the U.S. Coast Guard to make this a fixed bridge in order to minimize the cost of rehabilitation.

Type of bridge:Construction started:Opened to traffic:Length of main lift span:Number of railroad tracks:Clearance over mean high water (closed position):Clearance over mean high water (open position):Height of towers:Structural material:Tower material:Deck material (bridge and viaducts):Pier material:

SOURCES: "The Park Avenue Improvement in New York City," Scientific American (5/12/1894); The Bridges of New York by Sharon Reier, Quadrant Press (1977); "The Coming of the New York and Harlem Railroad" by Louis V. Grogan (1989); "A Guide to Civil Engineering Projects in and Around New York City," American Society of Civil Engineers (1997); MTA Metro-North Railroad; Peter Feigenbaum; David Jackino.